Diffusion transfer process



United States Patent 3,222,168 DIFFUSION TRANSFER PROCESS Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware No Drawing. Filed May 17, 1960, Ser. No. 29,593 Claims. (Cl. 96-29) This invention relates to photography and more particularly to processes and products for the formation of enlarged black-and-white or color images and employable in conjunction with photographic transfer procedures.

One object of the present invention is to provide processes whereby the area of one or more of the elements useful in photography for the carrying of images is appreciably expanded by suitable chemical and/or physical methods during and/or after photographic processing thereof so that there is or can be produced from the resultant expanded element, an enlarged or expanded positive image or print of good pictorial quality.

Another object of the invention is to provide processes whereby the area of a photosensitive element and/or image-receiving element useful in transfer photographic processes can be appreciably expanded so as to ultimately produce permanent enlarged positive images of .good quality.

Still another object of the invention is to provide imagereceiving elements useful in transfer photographic processes which can be appreciably and permanently expanded so that the positive image carried thereby is appreciably larger than its negative image.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products possessing the features, properties and the relation of elements which are exemplified in the following detailed description and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description.

In its broadest aspects, the invention is concerned with effecting, at a predetermined time, the appreciable expansion of an image-carrying element obtained by transfer photographic procedures, or, for that matter, by conventional photographic procedures, so as to produce enlarged black-and-white or color images. This broad concept is preferably carried out by the employment of an imageor printreceiving element capable of being appreciably expanded by suitable chemical and/or physi cal means during and/or after photographic processing thereof.

The present invention is particularly directed to the formation of expanded image-receiving elements carrying a positive image or print in black-and-white or in color, by diffusiontransfer techniques wherein an imagewise distribution of one or more image-forming components is formed in unexposed parts or less than completely exposed parts of a negative photosensitive element having one or more light-sensitive silver halide portions and transferred at least in part, to an imageor print-receiving element arranged in superimposed relation to the negative photosensitive element and wherein the image-receiving element during and/or after said image transfer is appreciably expanded and maintained in the expanded form or state.

The image-receiving elements of the present invention preferably comprise material capable of being appreciably 3,222,168 Patented Dec. 7, 1965 expanded and permanently maintained in the expanded state. The area of such material should be capable of expanding to a substantial degree so as to obtain the advantage of producing a sufficiently large positive image from a relatively small negative image. Moreover, the material once expanded and fixed in this state should not undergo shrinkage or reduction in area so as to reduce the size of the positive image carried thereby. Thus, the expanded image should maintain a relatively stable or fixed size. The preferable expansible materials are those which, once expanded, naturally and permanently retain the expanded state. However, it should be mentioned that materials which can be expanded and maintained or fixed in the expanded state by suitable means can also be employed.

The degree of expansion and hence the size of the enlargement depends upon such factors as the material employed and the attainment of an enlarged image of good contrast and resolution. Obviously, certain materials are more suited for specific degrees of expansion than others. Thus, the choice of any one of the preferred materials depends upon the expansion desired and upon the limits within which the expanded positive image retains good pictorial qualities.

A great number of materials are suitable for the present invention. In one preferred embodiment of the invention, materials capable of appreciable and permanent expansion are employed in a confined or compressed state so that upon relaxation or decompression by suitable chemical and/or physical means they readily expand. Among such materials which can be employed in a confined state as an image or print-receiving element and then released therefrom during and/ or after reception of an image are natural and synthetic polymeric materials or resins, as well as mixtures thereof where compatible. The compression or confinement of the preferred materials can be accomplished in various ways. For example, a solid rubber cylinder of a given diameter can. be stretched lengthwise so as to diminish its diameter to only a fraction of its unstretched area. Cross sectional layers of the solid rubber cylinder can be suitably fixed while in the stretched or compressed condition by such means as clamps, lamination to a support such as through the use of a releasable contact or pressure-sensitive adhesive, impregnation with an appropriate material which on hardening maintains the cross-sectional layer of rubber in its stressed condition and which hardened material is softened, dissolved or the like by such means as the photographic processing composition, heat and the like so as to permit the layer to undergo expansion readily and freely. These cross-sectional layers of the compressed rubber can be employed as positive image-receiving elements which, upon the formation of positive images thereon, are allowed to expand to their original area, that is, the area prior to stretching. Thus, an imagereceiving element of small area can be expanded to several times its compressed area to provide an enlarged positive image.

Instead of a rubber, suitable polymer or copolymer rods or solid cylinders can likewise be stretched to reduce the diameter thereof. For example, a solid cylinder of a linear polymer can be stretched to diminish its diameter to a much smaller diameter and fixed in this compressed or confined state by suitable means. One method of fixing cross-sectional layers of the linear polymer in the stretched or confined condition is by causing cross-linking to take place therein. Thus, during and/ or after the formation of the positive image thereon or therein, the cross linkage can be dissipated by chemical reaction to permit the layer to expand.

The fixing of the preferred polymeric materials in a confined state and/or the expansion thereof can also be accomplished by suitable heat treatment. For instance, it is possible to reduce or diminish the diameter of a solid cylinder or rod of a polymeric material which softens at a temperature somewhat above room temperature, for example, on the order of about 60 C. and above, by heating the cylinder to a temperature where it can be stretched. The resulting stretched polymeric rod of small area is maintained in this stretched or confined state until further treated for expansion. After using a layer of such polymeric material of diminished area for an image-receiving sheet or element, the same can be appreciably and permanently expanded by raising its temperature for a short period of time to a point where it can be expanded. For example, a rod of copolymer comprising, by weight, about 60 percent butyl methacrylate and about 40 percent methyl methacrylate was stretched about 300 percent. Sections perpendicular to the direction of elongation were taken. These sections when heated for about two minutes at 90 C. showed an increase of about 300 percent in surface area.

An advantage of employing such expansible image-receptive materials is that considerably smaller cameras can be employed, particularly those in which a transfer process occurs and yet adequately large prints or images can be obtained directly therefrom. For instance, in a diffusion transfer process, a small camera with a photosensitive element corresponding approximately to the size of an image-receiving element maintained in a confined or compressed state can be employed. A positive picture is produced in the camera on the image-receiving element which is then expanded several times its confined area upon removal from the camera.

Where the expansion is not immediate, such as by the release of mechanical restraining means such as clamps and the like, some specific aftertreatment may be necessary to insure expansion. As noted previously, that aftertreatment may be a simple chemical and/ or physical treatment such as heating, dissipation of cross-linkages, application of opposed tensional forces plus heat, and the like.

The expansion of the material is preferably uniform. However, it may also be possible through the use of suitable optics, for example, through the use of an anamorphic lens arrangement, to obtain a negative image in a photosensitive element and a reverse positive image thereof on an image-receiving element which can be uniformly expanded more in one direction than in the other without distortion of the image or images occurring.

In cases where the expanded positive image-carrying element is quite flexible, e.g., rubber, it can be made rigid or stiffened (after image formation and expansion) by coating either side with a suitable stiffening agent such as a polymeric material which readily hardens. In the event the coating is not applied to the back side but rather to the image-carrying side, then the coating should be transparent on hardening.

It should be mentioned that there can also be employed certain polymeric materials which when expanded do not naturally and permanently retain the expanded state but which must be fixed or treated to do so. For example, a sheet of a rubber of a given size can be employed as a positive image-receiving element. After formation of a positive image thereon, the rubber sheet can be stretched to a suitably enlarged size and fixed in the stretched state, for example by securing to a suitable rigid support by such means as clamps, hooks and the like or by laminating to a separate rigid support such as through the use of contact adhesives or by coating, impregnating or encasing it in an appropriate material, such as, for example, a polymeric plastic which on hardening forms a substantially rigid, transparent, stable casing. Acrylic resins such as polymethylmethacrylate, celluloses, epoxies, certain polyesters, polystyrene, certain vinyls and the like may be employed to fix or maintain materials of the above type in the expanded or stretched state. Obviously, other means for fixing the image-receiving element in the expanded state can also be employed.

Expanded image-receiving elements of a transparent nature which are to be viewed by reflected light rather than transmitted light can be provided with a suitable opaque background, for example, by applying to one side thereof an opaque coating of a white pigment such as titanium dioxide carried in a polymeric material which on hardening forms a rigid support or by laminating to a separate rigid white support such as through the use of contact adhesives. Obviously, other well-known means can be employed to provide a suitable viewing background.

It should also be pointed out that the present inventive concept may be employed in conjunction with the wellknown concepts or practices for the making of half-tone negatives and positives. Known practices for half-tone reproductions are shown, for example, in US. Patents Nos. 2,691,580, 2,691,583, 2,691,585 and 2,691,586. In the instant case, the positive image may be formed by the transfer of a screen or dot pattern. Such a pattern facilitates the expansion or stretching thereof without damage to the image.

One embodiment of the invention is set forth in the following non-limiting examples.

Example I An exposed silver halide emulsion was processed with a processing composition of the type described in Land US. Patent No. 2,662,822, and which, when solidified, provides the image-receiving layer, suitable silver precipitating agents being incorporated in the processing composition. The processing composition was spread between the exposed emulsion and a rubber dam, of the rubber dental dam type, which had been mounted on a temporary support to give the necessary rigidity for imbibition and processing. After an imbibition of approximately two rninutes, the superposed elements were separated and the rubber dam removed from the temporary support. It was found that the rubber sheet and soft film of processing composition thereon could be stretched in both directions without destroying the image.

Example 2 A rubber dam of the type referred to in Example 1 was coated with a solution of neoprene containing silver precipitating agents. When processed with a processing composition of the type described, for example, in US. Patent No. 2,543,181, which was superposed on an exposed silver halide emulsion for approximately two minutes, a silver image was formed in the layer of neoprene. When the processing composition and negative were removed from the superposed position it was found that the rubber dam and its neoprene image-receiving layer were stretchable without damage to the image.

Stripping coats of the type described for example, in US. Patent No. 2,883,122 may be applied over the neoprene image-receiving layer to prevent adhering of the residual processing composition to the neoprene imagereceiving layer.

Transfer processes involving the development of a latent image in a silver halide emulsion and the transfer of image-forming components from the emulsion to another layer to effect the formation of a print or image of the latent image in the other layer are now well known. In such processes, the latent image in a silver halide emulsion is developed and, concurrently with this development, alkali soluble image-forming components are transferred by diffusion or imbibition to a suitable imagereceiving element to form thereon or therein a positive image of the latent image. The above steps are preferably accomplished by spreading a thin film of a suitable liquid processing composition between a photosensitive element comprising a silver halide emulSlQB. and all image-receiving element, to form a lamination having a dry exterior and within which the positive imageforming reaction can take place.

Silver diifusion-transfer processes for producing blackand-white positive prints have been disclosed in a great number of my patents among which are US. Patents Nos. 2,543,181, 2,603,565, 2,662,822, 2,698,237, 2,698,- 245, 2,704,721 and 2,823,122. Transfer processes disclosing the formation of a positive image in color are found in US. Patents Nos. 2,559,643, 2,661,293, 2,698,- 244, 2,698,798 and 2,802,735.

In utilizing any of the expansible image-receiving elements to the end of providing a photographic image by diffusion-transfer processes, it is necessary to associate a photosensitive element with each image-receiving element. To facilitate production of a positive image on the expansible image-receiving element, especially in camera apparatus, each film unit comprising a photosensitive element and an expansible image-receiving element employs a rupturable container which is adapted to releasably hold at least an alkaline processing fluid or composition. The container, operationally secured to said film unit, is ruptured by suitable means such as when it moves between pressure rollers so as to cause the liquid contents of the container to be spread between superposed photosensitive and expansible image-receiving elements. Although the use of containers as mentioned above is especially suited for applying a liquid processing composition to the photosensitive element in a uniform layer as it is brought into superposed position with the image-receiving element, the photosensitive element may have the processing composition permeated therein by any of the many heretofore known procedures after which the photosensitive element may be positioned in superposed relation to the expansible image-receiving element.

The rupturable container, adapted to carry a liquid processing composition, is preferably positioned transversely of, and adhered to, the image-receiving element, although, if desired, it may be adhered to the photosensitive element. The container is also preferably of a length approximating the width of the film unit and is constructed to carry sufiicient liquid to effect negative image formation in exposed image areas of the photosensitive element and positive image formation in the corresponding image areas of the image-receiving element. Specific details of such containers are found, for example, in U.S. Patents Nos. 2,634,886, 2,653,732 and 2,750,075.

The liquid processing composition employed comprises at least an aqueous alkaline liquid of sufficient alkalinity to permit the developer to perform its developing function and, may, in certain cases, contain one or more photographic reagents therein. For instance, the processing liquid may contain one or more of the well-known developers necessary for the formation of black-andwhite or color images. Suitable developers for the composition are benzene derivatives having at least two hydroxyl and/or amino groups substituted in ortho or para position and the benzene nucleus, such as hydroquinone, Amidol (2,4-diaminophenol hydrochloride), Metol (1,4-methyl paraaminophenol sulfate), glycin (N- [1,4-hydroxyphenyl]-glycin), catechol, p-aminophenol and pyrogallol; and hydroxylamines; in particular primary and secondary aliphatic and aromatic N-substituted or li-hydroxylarnines which are soluble in aqueous alkali, including hydroxylamine, N-methyl hydroxylarnine, N- ethyl hydroxylamine and others described in US. Patent No. 2,857,276.

In silver transfer processes, the liquid processing composition may also contain a suitable silver halide solvent such as sodium thiosulfate, sodium thiocyanate, ammonium thiosulfate and others described in US. Patents Nos. 2,643,181 and 2,857,274.

While sodium hydroxide is, in general, the preferred alkali used in the processing liquid, other alkaline materials may be employed, for example, potassium or lithium hydroxide, sodium or potassium carbonate and diethylamine. If the liquid processing composition is to be applied in a relatively thin, uniform layer, it may also include a viscosity-increasing compound constituting filmforming material of the type which, when spread over a water-absorbent base and allowed to dry, will form a relatively firm and stable film. A preferred film-forming material is a high molecular weight polymer such as a polymeric, water-soluble ether inert to an alkali solution, as for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose. Other film-forming material or thickening agents for imparting a viscosity of to 200,000 centipoises at a temperature of 20 C. and Whose ability to increase viscosity is substantially unaffected when left in solution for a long period of time may also be used.

With reference to the materials useful for the formation of the photosensitive elements employed, it is to be observed that a wide selection of support materials is available. The support materials may be transparent or opaque and may comprise certain organic plastics, particularly those employed as film base materials, and may also employ paper. Specific examples of the support materials comprise cellulose esters such as, cellulose acetate, cellulose acetate butyrate, and the like, certain nylon type plastics, and baryta paper, i.e., a support having a baryta coating thereon.

The photosensitive material is provided by silver halide emulsions of the conventional character. Emulsion of suitable sensitivity rage is chosen to meet the particular requirement to use to which the photosensitive element will be put. The silver halide is in all instances used in a waterand alkali-permeable carrier material, such as for example, gelatin, although other water-alkali-permeable materials, known to the art, may be substituted. Examples of specific formulations of conventional emulsions suitable for such use are described in T. T. Baker, Photographic Emulsion Technique, American Publishing Company, Boston (1948), Chapter IV. When the photosensitive element is to be expanded alone or in conjunction with an image-receptive layer or element, it may be comprised of an expansible material such as those heretofore described in connection with image-receiving elements. When a photosensitive and image-receiving element are to be expanded or stretched together, the elements should be capable of expanding at substantially the same rate, under the same conditions and to the same extent. Integral photosensitive and image-receiving elements of the type described, for example, in copending application Serial No. 537,26l, filed September 28, 1955, and now US. Patent 2,944,894 is one instance where expansible elements may be employed and expanded together if desired.

The expansible image-receiving element may comprise a single sheet of an image-receptive material or it may comprise an expansible support which carries one or more layers or strata of expansible image-receptive material. Additionally the expansible image-receiving element may have incorporated therein one or more agents designed to facilitate the formation of the image. For example, in black-and-white processing, the image-receiving element may contain a suitable silver precipitating environment. Such an environment includes silver precipitating nuclei such as the heavy metal sulfides and/or selenides, the colloidal noble metals, and organic thio compounds. Other strata or layers such as shown in US. Patent No. 2,774,667, may also be employed in conjunction with the expansible image-receiving element.

In color transfer processes the expansible image-receiving element may contain one or more components for the production of color. The image-receiving element may comprise a single sheet of material which is dyeable from alkaline liquid or it may comprise a support upon which a layer or stratum of dyeable material is coated or otherwise afiixed. The image-receiving element may also contain agents to mordant or otherwise fix the dye image carried thereby.

It should be noted that the various strata or layers employed in conjunction with expansible image-receiving elements and heretofore mentioned should be such that each and every portion of the image-receiving elements are capable of expanding at substantially the same rate, under substantially the same conditions and to substantially the same extent.

It will be apparent that by appropriate selection of the image-receiving material from among the preferred expansible opaque and transparent materials it is possible to obtain either a positive reflection image or a positive transparency.

In addition to the preferred image-receiving elements described in detail above, a black-and-white silver positive image may also be formed in a layer or film of processing composition as shown in Example 1 or in a silver halide emulsion layer of a photosensitive element and then expanded to produce an enlarged image. In the production of a positive image in a layer or film of a processing composition, the expansion of the processing composition (image) layer and other layers associated therewith is achieved before the processing composition solidifies, that is, the expansion is accomplished while the processing composition is still soft. In this instance, silver precipitating nuclei are contained in the processing composition. A positive image can also be formed in the silver halide emulsion layer of a photosensitive element by incorporating silver precipitating nuclei therein, and providing a high covering power positive image and a negative of low covering power. Upon expansion of the photosensitive element the negative image undergoes an additional loss of covering power.

Having considered the general nature and construction of a film unit useful for carrying out the practices of this invention and comprising a photosensitive element, an expansible image-receiving element preferably adapted to be associated with said photosensitive element in superposed relation thereto and a container holding a liquid processing composition for processing said film unit after exposure thereof, a description of transfer reversal processes utilizing such a film unit and especially an expansible image-receiving element, will now be considered.

After exposure of the negative material or photosensitive element, the processing preferably proceeds by applying an alkaline processing composition to the exposed photosensitive element. This application, among other ways, can be made by spreading the alkaline processing composition between the photosensitive element and an image-receiving element from a rupturable container such as heretofore mentioned. The processing liquid applied to the photosensitive element migrates or permeates into the element and carries out its processing function or action. As the process proceeds the latent silver halide image is developed. As a result or function of the development of latent silver halide to silver there is formed a soluble, imagewise distribution of image-forming components which, at least in part, is transferred from the photosensitive element in its liquid solvent or carrier and deposited upon an expansible image-receiving element of the type herein described. For example, in the formation of a color image, a conventional coupler present in solution in alkaline liquid in the photosensitive element is reacted with the oxidation product of a silver halide color developer also present in the element to form a dye image in situ with the developed silver, while providing an imagewise distribution of unreacted coupler and developer. Similarly, in the formation of a silver image, a silver halide solvent or transfer agent permeated into the photosensitive element becomes available to form an imagewise distribution of a soluble and ditfusible silver complex as a function to the development of latent image silver halide to silver.

In other words, the development of latent image silver halide to silver is utilized to form, in the unexposed and less than completely exposed portions of a silver halide layer, a differential or imagewise distribution of at least one photographic reagent which is soluble or dispersible in liquid processing composition in the layer and is therefore diffusible from the photosensitive element, while the silver development in the photosensitive layer is utilized to render said reagent immobile or ineffective in portions of the layer wherein development of latent image silver halide takes place.

In one preferred embodiment, after the transfer or diffusion of the image-forming components from the photosensitive element to an image-receiving element located in superposed and closely adjacent relation to the photosensitive element, the expansible image-receiving element carrying the desired positive image is stripped from the photo-sensitive element and appreciably expanded. In the case of film units or packs wherein the photosensitive element and expansible image-receiving element are removed from the camera in superposed relation such as shown in US. Patent No. 2,495,111, the expansible imagereceiving element at the end of the imbibition period may be stripped from the photosensitive element and suitably expanded as above, or both the photosensitive element and image-receiving element after removal of the camera may be suitably expanded together during and/ or after the imbibition or transfer period.

Since certain changes may be made in the above processes and products without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process of forming photographic images by diffusion transfer, said process including the steps of exposing a silver halide emulsion, applying an aqueous alkaline solution to said exposed silver halide emulsion to effect development thereof, and forming, as a function of said development, an imagewise distribution of a diffusible image-forming component, transferring by diffusion at least part of said imagewise distribution of diffusible image-forming components to a superposed imagecarrying layer to form a visible transfer image, said imagecarrying layer having length, width and thickness and being adapted to be expanded and comprising a member selected from the group consisting of (a) rubber and (b) a 60:40 butyl methacrylate/methyl methacrylate copolymer, and substantially expanding said image-carrying layer in at least one of its length and width dimensions thereby providing a transfer image substantially enlarged as compared with the initially formed transfer image.

2. The process of claim 1, wherein said image-carrying layer comprises rubber, said expanding is effected by mechanically stretching said image-carrier layer, and said enlarged image is afiixed to a support to thereby maintain said enlarged image in its expanded state.

3. The process of claim 1, wherein said transfer image is a half-tone image.

4. The process of claim 1, wherein said image-carrying layer comprises a support of rubber carrying a stratum of rubber containing a silver precipitating agent, said diffusible image-forming component is a soluble silver complex, and said visible transfer image is a silver image.

5. The process of claim 1, wherein said image-carrying layer comprises a 60:40 butyl methacrylate/methyl methacrylate copolymer and said expanding is effected by heating.

References Cited by the Examiner UNITED STATES PATENTS 2,117,321 5/1938 Hill. 2,575,970 11/1951 Nagel 9646 X 2,643,598 6/1953 Carroll 9646 X (Other references on following page) 9 10 UNITED STATES PATENTS 19,810 1893 Great Britain. 2 53 527 9/1953 Land 96 29 523, 58 7/1940 Great Britain. 2,704,721 3/1955 Land 96 9 OTHER REFERENCES 2,923,623 2/1960 Land 96-29 Land, one Ste p Photography, The Photographic Jour- 3026648 3/1962 Lemelsen 96 '1 X 5 nal, Section A, January 1950, pages 7-15.

FOREIGN PATENTS NORMAN G. TORCHIN, Primary Examiner.

15,217 1894 Great Britain. MILTON STERMAN, PHILIP E. MAGNAN, LOUISE 16,125 1891 Great Britain. P. QUAST, Examiners. 

1. A PROCESS OF FORMING PHOTOGRAPHIC IMAGES BY DIFFUSION TRANSFER, SAID PROCESS INCLUDING THE STEPS OF EXPOSING A SILVER HALIDE EMULSION, APPLYING AN AQUEOUS ALKALINE SOLUTION TO SAID EXPOSED SILVER HALIDE EMULSION TO EFFECT DEVELOPMENT THEREOF, AND FORMING AS A FUNCTION OF SAID DEVELOPMENT, AN IMAGEWISE DISTRIBUTION OF A DIFFUSIBLE IMAGE-FORMING COMPONENT, TRANSFERRING BY DIFFUSION AT LEAST PART OF SAID IMAGEWISE DISTRIBUTION OF DIFFUSIBLE IMAGE-FORMING COMPONENTS TO A SUPERPOSED IMAGECARRYING LAYER TO FORM A VISIBLE TRANSFER IMAGE, SAID IMAGECARRYING LAYER HAVING LENGTH, WIDTH AND THICKNESS AND BEING ADAPTED TO BE EXPANDED AND COMPRISING A MEMBER SELECTED FROM THE GROUP CONSISTING OF (A) RUBBER AND (B) A 60:40 BUTYL METHACRYLATE/METHYL METHACRYLATE COPOLYMER, AND SUBSTANTIALLY EXPANDING SAID IMAGE-CARRYING LAYER IN AT LEAST ONE OF ITS LENGTH AND WIDTH DIMENSIONS THEREBY PROVIDING A TRANSFER IMAGE SUBSTANTIALLY ENLARGED AS COMPARED WITH THE INITIALLY FORMED TRANSFER IMAGE. 